The math of say 10 sec max queueing vs say 5min wait time is pretty straight forward but maybe not intuitive. You pay significant (30%+ sometimes, depends on volume) overhead for those last minutes (queueing theory, Erlang C formula). For that reason, it's nice to do something like this. Low customer effort cost but high savings.

Virtual queueing through the phone is a bit meh, you still have to pick up the phone in the first place. Doing it through the web though gives imo a less annoying experience - wait time less visible and only have to pick up the phone once.